Ram air turbines are commonly used in military and commercial aircraft to provide a source of hydraulic or electrical power in the event of an emergency. Modern aircraft generate power through the main engines or via an auxiliary power unit such as a fuel-burning turbine typically located in the tail of the aircraft. In most applications for commercial aircraft, ram air turbines are retracted into the fuselage or wing(s) under normal operating conditions, but are deployed in the event of an emergency loss of power. They typically comprise two or more blades, much like windmill blades, carried by a shaft which is coupled to a generator. The blades rotate the shaft in response to contact with the air stream produced by movement of the aircraft during flight. Depending upon the size of the blades, the capacity of the electrical generator and the flight speed of the aircraft, ram air turbines can supply as much as 70 kW for use in powering flight controls, linked hydraulics and flight-critical instrumentation.
Military aircraft, particularly those designed for electronic warfare, have in the past typically used ram air turbines externally mounted to a pod to deliver power for electronic equipment employed to counter enemy air defenses using reactive and/or pre-emptive jamming techniques, to provide stand-off escort jamming, to initiate electronic attacks and to provide self-protection capability for the aircraft. A pod is essentially a generally cylindrical, aerodynamically-shaped housing mounted to the underside of the aircraft wings. More recently, submerged ram air turbines have been proposed as a replacement for externally mounted designs. The term “submerged” in this context refers to the placement of ram air turbines within the interior of pods in alignment with one or more inlets which direct a flow of air onto the blades of the turbine which is then exhausted through the pod outlet(s).
The increasing sophistication of electronic equipment employed in military aircraft has created a requirement for additional power at flight speeds of 200 to 220 knots. Existing externally mounted and submerged ram air turbines do not provide sufficient power output, and there is a need for an improved ram air turbine generating system.